Long-term Follow-up of Patients with Spasmodic Dysphonia Repeatedly Treated with Botulinum Toxin Injections

Adductor spasmodic dysphonia (SD) is a focal laryngeal dystonia mainly resulting in a strained voice quality with spastic voice breaks and frequency shifts, perturbing fluency and intelligibility. SD-patients report unusually high impairment of their quality of life. The standard treatment is botulinum toxin injection in the thyroarytenoid muscles, in order to interfere with the perturbed sensory feedback loop of kinetic muscle tension regulation. The globally favorable effects are temporary, but the botulinum injections can be repeated. There is a lack of information about long-term effects. This is the first study investigating effects over several years, and comparing self-evaluation of patients with objective multimodal acoustic analysis. Results show that 72% of the individual injections are successful. The effects of botulinum are not reduced after repeated injections. In contrary, the self-perceived improvement increases in average over time. When self-evaluations preinjection are considered, patients tend to evaluate their voice and their handicap as worsening over time. This contrasts with the results of multimodal acoustic analysis. Objective data reveal a relative stability over time for as well preas postinjection. This seems to indicate that there is no shift over time in the objective severity of deviance in voice quality.